Repair of intra-membranous bone fractures and defects in rats. Immunolocalization of bone and cartilage proteins and proteoglycans

Biomaterials for Regenerative Cranioplasty: Current State of Clinical Application and Future Challenges

Acquired cranial defects are a prevalent condition in neurosurgery and call for cranioplasty, where the missing or defective cranium is replaced by an implant. Nevertheless, the biomaterials in current clinical applications are hardly exempt from long-term safety and comfort concerns. An appealing solution is regenerative cranioplasty, where biomaterials with/without cells and bioactive molecules are applied to induce the regeneration of the cranium and ultimately repair the cranial defects. This review examines the current state of research, development, and translational application of regenerative cranioplasty biomaterials and discusses the efforts required in future research. The first section briefly introduced the regenerative capacity of the cranium, including the spontaneous bone regeneration bioactivities and the presence of pluripotent skeletal stem cells in the cranial suture. Then, three major types of biomaterials for regenerative cranioplasty, namely the calcium phosphate/titanium (CaP/Ti) composites, mineralised collagen, and 3D-printed polycaprolactone (PCL) composites, are reviewed for their composition, material properties, and findings from clinical trials. The third part discusses perspectives on future research and development of regenerative cranioplasty biomaterials, with a considerable portion based on issues identified in clinical trials. This review aims to facilitate the development of biomaterials that ultimately contribute to a safer and more effective healing of cranial defects.

Skull Fracture Healing in Children Up To 36 Months - A Cohort Analysis

During medicolegal proceedings in cases of suspected child abuse it is sometimes argued that skull fractures could be sequelae from complications at birth or resulted from a prior witnessed accidental trauma that may have preceded the suspected abusive event. There is paucity of scientific evidence indicating timing for skull fracture healing in children up to 36 months old. Objective of this study was to assess the average time to imaging documentation of skull fracture healing in children up to 36 months old. We performed retrospective chart review and image analysis in children with documented skull fractures after trauma between May 2009 and December 2014, excluding any patients who underwent cranial procedures related to the head injury, patients with pre-existing CSF shunts, patients who were referred for child abuse evaluation, and patients who were admitted to the General Surgery service for multi-organ trauma.We analyzed 185 skull fractures: 82 fractures were not healed, 49 fractures were partially healed, and 54 fractures were healed on follow-up imaging. The mean time to imaging evidence of healing among patients with healed fractures was 108 days (3.6 months), the median was 112 days (3.7 months), the minimum was 22 days, and the maximum was 225 days (7.5 months). Chi-square analysis showed a significant relationship between the skull fracture healed status and presence of bleed (P = 0.001) and with fracture characteristics of displaced, depressed, or dehiscent (P= 0.009). There was no significant association with the age group (P= 0.32) nor with involvement of multiple cranial plates (P= 0.73). This information may be useful during medicolegal proceedings in patients with suspected abusive head trauma mechanism.

Effect of compression on mandibular fracture haematoma-derived cells

Mechanical stress induces a variety of biochemical and morphological reactions in bone cell biology. This study aimed to investigate appropriate pressures of osteogenesis on the biological responses of 3-dimensional cultured human mandibular fracture haematoma-derived cells by compressive loading. Six patients with mandibular fractures who underwent open reduction and internal fixation were included in the study. During the operation, fracture haematomas that formed fibrin clots were manually removed before irrigation. First, pressures were applied to human mandibular fracture haematoma-derived cell-seeded collagen sponges. The sponges were subjected to mechanical compression using loading equipment applied at no compression, 0.5, or 1 mm. Compressive loading was applied to the samples prior to compression for 0, 6, 12, or 24 hours. Collagen sponge samples were collected for quantification of mRNA using several parameters including alkaline phosphatase (ALP), osteopontin (OPN), osterix (OSX), runt-related gene 2 (RUNX2), protein level, and immunocytochemistry (anti-sclerostin). Among these the 0.5 mm compression group compared with the control and 1.0 mm compression groups upregulated mRNA expression of OPN and OSX after 24 hours. Additionally, compared with the control group, a significantly higher OSX gene expression was observed in both the 0.5 mm and 1.0 mm groups after 6, 12, and 24 hours of compression (p < 0.05). However, no significant differences were observed regarding ALP and RUNX2 expression. These results indicated increased stimulation of osteogenesis of the mandibular fracture-line gap in the 0.5 mm compression group compared with the control and 1.0 mm compression groups.

Selection of animal models for pre-clinical strategies in evaluating the fracture healing, bone graft substitutes and bone tissue regeneration and engineering

In vitro assays can be useful in determining biological mechanism and optimizing scaffold parameters, however translation of the in vitro results to clinics is generally hard. Animal experimentation is a better approximation than in vitro tests, and usage of animal models is often essential in extrapolating the experimental results and translating the information in a human clinical setting. In addition, usage of animal models to study fracture healing is useful to answer questions related to the most effective method to treat humans. There are several factors that should be considered when selecting an animal model. These include availability of the animal, cost, ease of handling and care, size of the animal, acceptability to society, resistance to surgery, infection and disease, biological properties analogous to humans, bone structure and composition, as well as bone modeling and remodeling characteristics. Animal experiments on bone healing have been conducted on small and large animals, including mice, rats, rabbits, dogs, pigs, goats and sheep. This review also describes the molecular events during various steps of fracture healing and explains different means of fracture healing evaluation including biomechanical, histopathological and radiological assessments.

Comparison of bone formation ingrafted periosteum harvested from tibia and calvaria

Periosteum covers the bone surface and displays the potential to initiate bone formation, after injury to the bone. Numerous studies have demonstrated that the periosteum plays major roles in the healing process after bone fracture. Some reports have described that in the healing of long bone fractures, the periosteum forms new bone by intramembranous and endochondral ossification. Other researchers insist that healing of defects in membrane bone shows bone formation by intramembranous ossification. However, previous studies have not been able to clarify differences in bone formation patterns. We hypothesized that differences in bone formation pattern are associated with the periosteal potential for cell differentiation. The present study grafted periosteum, harvested from the tibia and calvaria, into the suprahyoid muscle, with the aim of interrupting release of factors from bone matrix. Bone formation, after grafting periosteum, harvested from the tibia and calvaria, was examined histologically and radiographically. Grafted tibial periosteum formed a large area of new bone by intramembranous and endochondral ossification, while grafted calvarial periosteum displayed intramembranous ossification. Grafted tibial periosteum formed a larger area of bone than grafted calvarial periosteum. Patterns of cell differentiation thus differ between grafted periosteum, harvested from the tibia and calvaria.

A mouse model of mandibular osteotomy healing

The purpose of this study was to establish a novel mouse model of membranous osteotomy healing. By applying this model to transgenic mice or using in situ hybridization techniques, we can subsequently investigate candidate genes that are believed to be important in membranous osteotomy healing. In the current study, 20 adult male CD-1 mice underwent a full-thickness osteotomy between the second and third molars of the right hemimandible using a 3-mm diamond disc and copious irrigation. Compo-Post pins were secured into the mandible, 2 mm anterior and posterior to the osteotomy. After the soft tissues were reapproximated and the skin was closed, an acrylic external fixator was attached to the exposed posts for stabilization. The animals were killed on postoperative day number 7, 10, 14, and 28 (n=5 animals per time point). The right hemimandibles were decalcified and embedded in paraffin for histologic evaluation or immunohistochemistry localizing osteocalcin. At 7 days after the osteotomy, early intramembranous bone formation could be seen extending from either edge of the osteotomized bone. By 10 days, an increasing number of small blood vessels could be seen within and around the osteotomy. At 14 days, the bone edges were in close approximation, and by 28 days the callus had been replaced by actively remodeling woven bone in all specimens examined. Immunohistochemistry demonstrated that osteocalcin expression correlated temporally with the transition from a soft to a hard callus. Furthermore, osteocalcin was spatially confined to osteoblasts actively laying down new osteoid or remodeling bone. This study describes a novel mouse model of membranous osteotomy healing that can be used as a paradigm for future osteotomy healing studies investigating candidate genes critical for osteogenesis and successful bone repair.

Experimental study of reconstruction of the temporomandibular joint using a bone transport technique

PURPOSE

This study investigated the applicability of transport distraction osteogenesis with an internal appliance for reconstruction of the temporomandibular joint (TMJ).

MATERIALS AND METHODS

Fifteen millimeters of the ascending ramus, including the condyle and intra-articular disc, was extirpated in 42 white rabbits (3.0 kg weight). After an L-osteotomy was performed from the anterior border of the coronoid process to the posterior border of the mandible, an internal distraction appliance was applied. The transport segment was advanced 0.9 mm/day for 14 days after a 14-day healing period. During a 24-week period after the completion of the lengthening, the rabbits were killed at various intervals.

RESULTS

Eight weeks after the completion of the lengthening, the distraction gap between the transport segment and the preexisting mandible was indistinguishable in the radiographs. New bone and a large amount of cartilage were observed microscopically in the distraction gap. New bone was also observed at the leading edge of the transport segment. This bone seemed to form from the surrounding periosteum. At 8 weeks after the completion of lengthening, the mature cortical bone was reconstructed. A collagenous-like structure formed a cap over the leading edge of the transport segment. This cap may substitute for an articular disc. The new bone remodeled and resembled the condyle.

CONCLUSION

The bone transport technique is promising for the reconstruction of TMJ.

Healing response to various forms of human demineralized bone matrix in athymic rat cranial defects

PURPOSE

This study compared the ability of a bone autograft and four distinct forms of human demineralized bone (DBM) to elicit bone repair in a critical size cranial defect in athymic rats.

MATERIALS AND METHODS

Cranial defects were created in athymic rats and then grafted with either an autograft, rat DBM particles in glycerol (rGel), or one of four forms of human DBM: 1) hGel; 2) Putty (DBM fibers in glycerol); 3) Sheet (sheet of DBM fibers); or 4) Flex (DBM fiber sheet with glycerol). Histology, histomorphometry, and radiographic density of the graft sites were evaluated at 8 weeks.

RESULTS

Of the grafted defects, 29% to 58% were found to be filled with new bone. The rGel and human forms of DBM stimulated similar amounts of new bone growth in comparison with the autograft-filled defects. The fiber-based grafts produced the largest amounts of new bone.

CONCLUSIONS

Human DBM in gel, putty and sheet forms were found to perform as well as an autograft in a critical size cranial defect in the athymic rat.

Influence of surrounding soft tissues on onlay bone graft incorporation

OBJECTIVES

This investigation aimed to evaluate the influence of three different soft tissue environments on onlay bone graft incorporation into the craniomaxillofacial skeleton and to follow this process immunohistochemically by staining for some bone and cartilage matrix proteins and proteoglycans.

STUDY DESIGN

Femoral and tibial bone grafts, either uni- or bicortical, were placed subperiosteally, submuscularly, and intramuscularly in 36 identically sized and aged isogeneic rats. The results were evaluated after 4, 12, and 20 weeks.

RESULTS

Corticocancellous grafts showed a more extensive incorporation and more pronounced local resorption. Bicortical grafts produced more resorption of the recipient site, which oftentimes resulted in the graft being almost level with the surrounding bone. The marrow space of both graft types was sealed off by compact bone formation. Intense labeling of tested bone matrix proteins at various parts of the graft-host area was demonstrated. Ultimate graft height was significantly reduced for most groups, but no major differences between groups were registered. Intramuscularly positioned control grafts ultimately showed signs of lacking viability and reduced labeling of cartilage matrix proteins.

CONCLUSIONS

These findings indicate that either type of graft had its drawbacks and that further studies to enhance integration and size maintenance are necessary to improve overall graft persistence. Immunolabeling may help to identify essential mechanisms in and find markers of graft incorporation.

Insulin enhancement of in vitro wound healing in fetal rat parietal bones

PURPOSE

This study evaluated the effect of insulin on fracture in fetal rat intramembranous bone using an organ culture system in which bone mineralizes in vitro.

MATERIALS AND METHODS

Twenty-day-old fetal rat parietal bones were fractured parallel to the frontal plane and cultured in a serum-free medium with or without insulin for 4 to 12 days. They were then processed for light microscopy.

RESULTS

In the specimens not treated with insulin, bony bridges were observed in less than 10% on day 4 and 8, and only 45% on day 12. In bones treated with insulin at 10(-6) mol/L, bony bridges were observed in 73% on day 4 and 100% on day 8 and 12. No callus or cartilage formation was observed during the wound repair process, indicating that intramembranous ossification occurred.

CONCLUSION

These findings suggest that insulin has a direct effect on bone cells, which enhances the healing of fractures in intramembranous bone.

Localization of the mRNA for bone matrix proteins during fracture healing as determined by in situ hybridization

The expression of the mRNAs for osteonectin (ON), osteopontin (OPN), osteocalcin (OC), and matrix Gla protein (MGP) was studied by in situ hybridization during the healing process of an experimental fracture in adult rat femora. At day 1 postoperatively, ON mRNA was detected in the proliferating periosteum. At day 3, ON, OPN, and OC mRNAs were detected in woven bone. From day 5, MGP and ON mRNAs were detected in the immature chondrocytes. From day 7, ON, OPN, and OC mRNAs were detected in the osteoblastic cells in newly formed endosteal trabecular bone. OPN mRNA was also detected in some of the osteocytes in trabecular bone. From day 14, OPN and MGP mRNAs were detected in newly formed periosteal hypertrophic chondrocytes, and the ON, OPN, and OC mRNAs were detected in osteoblastic cells in newly formed periosteal trabecular bone. Although the cell types that expressed each mRNA in fractured bones were similar to those in embryonic bones, the time course of these mRNA expression in fractured bones was different from that in embryonic bones. We considered that this system is useful to investigate the phenotypic change in osteogenic and chondrogenic lineage cells that appears during fracture healing at the molecular level.

Ectomesenchymal mandibular symphysis bone graft: an improvement in alveolar cleft grafting?

Bone grafting the alveolar cleft in cleft lip and palate (CLP) patients is widely accepted. A traditional graft is the iliac crest. Other bone graft donor sites are briefly discussed. The ratio for an ectomesenchymal bone graft in alveolar cleft repair is explained. Aspects of the embryology, bone graft physiology, and reports on mandibular symphysis bone grafting are discussed.